Here is described the first dinosaur evidence from Chiapas, and also the southernmost evidence of dinosaurs in Mexico. A small theropod tooth, identified as Richardoestesia isosceles, based on its shape and the presence of small denticles on the mesial and distal carinae with rounded outline, was collected in the Ocozocoautla Formation (Late Cretaceous, Maastrichtian). These results extend the fossil record of this taxon in North America, as it is the southernmost record of Richardoestesia and the first report of this genus in Mexico.